A transmission is applied as an apparatus to change speeds of a rotational drive force that a motor such as an engine mounted to a vehicle outputs. As a transmission for a vehicle, for example, Patent reference 1 discloses a transmission that includes four planetary mechanisms rotatably supported about a rotation axis, four clutches selectively connecting predetermined elements at the planetary mechanisms, and two brakes braking rotations of predetermined elements at the planetary mechanisms. According to the layout of each member disclosed in Patent reference 1, by multiply operating three engaging elements among four clutches and two brakes, speed stages constructed with ten forward speeds and one rearward speed can be established.
The transmission including those plural planetary mechanisms and engaging elements is advantageous in terms of capable of obtaining multiple speed stages with a relatively small sized body structure because of features of the planetary mechanisms. On the other hand, according to those transmissions, the number of elements that should be connected from an input side to an output side is large, thus variety of layout patterns are applied. Accordingly, because respective layouts have different features, the optimum layout design is provided in terms of use of the transmission, required performance, and manufacturing costs, for example.
The transmission may be required to further increase the number of speed stages in accordance with changes in uses. In those circumstances, layouts of the transmission that can establish multiple speed stages exceeding ten forward speeds can be designed by increasing engagement patterns that are combinations of engaging elements in operation. However, considering diversions of parts, it is more favorable that the number of speed stages can be further increased only by adding engaging elements to an existing transmission than newly designing layouts.
Thereupon, it is postulated that the number of speed stages is further increased by increasing the number of brakes in Patent reference 1. In case of increasing the number of brakes, a connection member among connection members connecting elements between the elements serves as an object, the connection member where another member is not interposed between the connection member and a housing, the connection member which is always connected to one of the elements, and the connection member excluding the connection member that is provided to another brake. In that case, provided that a brake is added to a connection member (42) that connects a sun gear (14A) of a second planetary gear set and an end of a clutch (30) in FIG. 2 of Patent reference 1, an engagement pattern for braking the rotation of the sun gear via the connection member (42) can be added.
In the foregoing construction, three speed stages are added by an increase in the engagement pattern. However, provided that the maximum number of the engaging elements that are switched when transiting to an adjacent speed stage is defined as two, the number of the added speed stages is two. It is considered that this is caused because the layout designing according to Patent reference 1 is not conducted in terms of expandability foreseeing further increases in the number of speed stages of the transmission, and is conducted in terms of a predetermined required performance.
A purpose is to provide a transmission that can establish multiple speed stages with a layout that is different from conventional layouts and that can enhance expandability.